1. Field of the Invention
The present invention relates to the field of electrical machines. It relates to a laminated stator body for a rotating electrical machine.
Such an electrical machine is disclosed, for example, by xe2x80x9cKonstruktion elektrischer Maschinenxe2x80x9d [xe2x80x9cConstruction of electrical machinesxe2x80x9d], E. Wiedemann and W. Kellenberger, Springer-Verlag, Berlin/Heidelberg, 1967, pages 337-339.
2. Discussion of Background
In rotating alternating-current machines, such as, for example, generators or motors, magnetic fields rotate in operation at the frequency of the rotational speed. These fields attempt to change the laminated stator body into a rotating ellipse in the case of two-pole machines and into a rotating square in the case of four-pole machines. These deformations of the laminated stator body are the cause of magnetic noises and of vibrations of the stator casing. In this case, however, these deformations are also directly related to the geometric proportions of the laminated stator body. Contributory variables are the outside diameter of the laminated stator body and the yoke height of the laminated body. The depth of the slots for accommodating the stator winding, which are distributed over the inner circumference of the bore and are oriented to the longitudinal axis of the machine, also has an effect.
Typical designs of 2-pole generators with their so-called 4-node vibrations of the laminated stator body, which occur under operating conditions, make it necessary for the laminated body to be arranged resiliently in a stator casing. However, the utilization of the resilient arrangement is limited not least by the strength of the stator winding overhangs arranged outside the laminated stator body.
The use of generators as turbomachines in high-voltage networks is especially problematicalxe2x80x94and the essence of the present invention is also directed at this problemxe2x80x94, the term high voltage referring here to a far higher voltage than the operating voltages of 20-30 kV which are common today. Such high-voltage generators are used in a voltage range of up to 400 kV or higher and are connected directlyxe2x80x94that is, without the interconnection of a transformerxe2x80x94to a power transmission network having a conventional voltage level of, for example, 400 kV. The advantages of a direct network connection lie in particular in the saving of transformers and associated switchgear, including installation space and maintenance cost.
In high-voltage generators, however, a larger number of turns than in conventional machines is a basic precondition. The larger number of turns must therefore be inserted in deeper slots of a laminated stator body. In publication JP 1-126141, the notches are filled with a permeable material, which, however, means that more material is required and thus the costs are higher.
In the case of the yoke heightxe2x80x94that is, the distance between the slot root and the outside diameter of the laminated stator bodyxe2x80x94the dimension, in view of the magnetic flux flowing through, must not fall below a minimum. However, the combination of deep stator slots and yoke heights designed with regard to the flux density leads to operation in the vicinity of the 4-node natural frequency and thus to inadmissible amplitudes at the abovementioned 4-node vibrations. The amplitudes of the vibrations would increase up to an order of magnitude of 150 m, which may lead to the mechanical destruction of the electrical machine. In terms of economical transport, strengthening the laminated stator body by increasing the diameter, is limited by the so-called track loading gage.
Accordingly, one object of the invention is to design a novel laminated stator body for a high-voltage turbogenerator of the type mentioned at the beginning in such a way that, with a comparatively small outside diameter of the laminated stator body and large slot depths for the stator winding, a sufficiently high mechanical strength in respect of operationally induced vibration amplitudes is achieved.
According to the invention, the object is achieved by the features of the first claim.
The advantages of the invention may be seen, inter alia, in the fact that, by virtue of the notches on the radial outside of the segmental laminations forming the laminated stator body, the natural frequency of the laminated body is considerably reduced and comes to lie below the rotational excitation frequency, whereas the magnetic conditions in the laminated body remain largely unaffected. The notches are not filled with a permeable material, as in the prior, art but are filled with air. Here, the notching permits a comparatively small diameter of the laminated stator body, which comprises the magnetic part of a high-voltage generator having deep slots for the conductor bars or conductor coils. It is especially advantageous if the notches end radially on the inside in a relief opening.
A first preferred embodiment of the invention is defined in that twice the number of notches as slots for the stator winding are arranged in the laminated stator body, the notch depth being in the order of magnitude of 20% of the yoke height.
A second preferred embodiment of the laminated stator body according to the invention is distinguished in that the number of slots and notches in the laminated stator body is the same, the notch depth being in the order of magnitude of 40% of the yoke height.
A width of the notches of about 0.5 mm to 1 mm is especially preferred.